1. Field of the Invention
The present disclosure relates generally to methods and active materials for purifying gas streams containing halide as a contaminant, for example, in amounts as low as parts-per-million (ppm) or even parts-per-billion (ppb).
2. Technical Background
Halogen products and byproducts present a serious problem in the chemical industry by causing, among other things, deactivation of downstream catalysts and corrosion of equipment. For example, in ammonia and hydrogen manufacturing, halide such as hydrogen chloride can significantly reduce process efficiency by poisoning a variety of catalysts such as reformer catalysts, high-temperature shift catalysts, Fischer-Tropsch catalysts and, in particular, copper-based low-temperature shift catalysts. In fact, less than 1 ppm halide can severely deactivate downstream catalysts in ammonia and hydrogen plants, especially copper-based catalysts. Thus, it is desirable to remove any halide present in the gas stream before it comes in contact with the catalysts.
The removal of relatively large amounts of halide from gas streams using metal sorbents such as Ca-based materials, Mg-based materials, Mn-based materials, Zn-based materials and alkaline-based materials has been previously disclosed. While these sorbents can strip large amounts of halide, they are less effective in removing very low amounts of halogen from a gas stream; i.e. the lower the halogen content in the gas stream, the more difficult it is to remove it.
There remains a need for methods and active materials that can remove halide even when it is present at low levels in a gas stream,